Color filter structure of color image sensor

ABSTRACT

There is provided an improvement on a solid-state type color image sensor having a color filter arrangement matching the line sequential color difference signal method. A color filter selected from magenta, yellow and cyan for covering the entire area of each picture cell and a color filter of a different color are superposed one upon the other. The color filters covering predetermined ratios of the areas of associated picture cells are preferably formed collectively in a stripe shape.

BACKGROUND OF THE INVENTION

The present invention relates to a solid-state color image sensor and amethod of manufacturing the same, for use particularly with anelectronic still camera.

A solid-state color image sensor has photoelectric conversion cellsarranged in a matrix configuration and associated color filters to pickup color signals.

Various color image pickup methods have been proposed heretofore,including such as a tri-plate type method with color separation intothree primaries of red, green and blue. Conventional color image pickupmethods have been found not satisfactory in sensitivity. A new methodsolving this problem is known as a line sequential color differencesignal method, which is described, for example, by Khono et al. in"Perfect Line Sequential Color Difference Signal and Mono-plate Method",The Institute of Television Engineers of Japan, Technical Report ED836(February, 1985, and by Shin Fujimoto in "Camera System", Journal of theInstitute of Television Engineers of Japan, Vol. 40, No. 11, p. 1073,1986. With this method, color signals can be obtained line-sequentiallyand alternately in the form of color difference signals. This methodadopts a field integration mode or a frame integration method to readimage signals.

The arrangements of color filters used in the field integration mode andthe frame integration mode are shown in FIG. 1.

An image sensor used in the field integration mode is constructed suchthat color filters of magenta (Mg) cyan (Cy), green (G) and cyan aredisposed in this order in the 1st column (1), color filters of green,yellow (Ye), magenta and yellow are disposed in this order in the 2ndcolumn (2), and the two columns with such color filter arrangement arealternately disposed over the whole area of the sensor. In order to readcolor signals from the sensor with an arrangement of one filter perpicture cell, a mixed column readout method is used whereby at the 1stfield defining a certain scan line, both the rows (a) and (b) are readout together to obtain a sum of Mg+Cy signal and G+Ye signal, and at the2nd field defining the next scan line, both the rows (b) and (c) areread out together to obtain a sum of Cy+G signal and Ye+Mg signal. Eachphotoelectric conversion area is formed in alignment with the center ofeach color filter. The green (G) filter is obtained by superposing theyellow and cyan filters.

Although the main trend of current video cameras adopts the mixed columnreadout method, the image resolution thereof is dependent on the size ofpicture cell so that its vertical resolution is not sufficient for beingused by electronic still cameras which require a high resolution.

FIG. 1 shows the arrangement of color filters used in the frameintegration mode. Each color filter provided for each picture cell isconstructed of two color filters each being a half size as that used inthe field integration mode. At the row (a) an Mg/Cy filter and a G/Yefilter are alternately disposed, and at the (b) line a Cy/G filter andan Ye/Mg filter are alternately disposed. In reading color signals, eachframe is read in unit of one line such that at the row (a) of the 1stframe, signals Mg+Cy and G+Ye are obtained and at the row (b) of the 2ndframe, signals Cy+G and Ye+Mg are obtained.

However, the material such as casein of a color filter used in the frameintegration mode has a poor resolution and hence poor alignmentprecision at the joint between two halves of the color filter. Theobtained color filter may therefore operate stronger at one color thanat the other color so that flicker noises are superposed on colordifference signals.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a solid-state colorimage sensor capable of obtaining a stable and good vertical resolution.

It is another object of the present invention to provide a solid-statecolor image sensor capable of obtaining color difference signals withless noises.

It is a further object of the present invention to provide a method ofmanufacturing a solid-state color image sensor as above.

According to one aspect of the present invention, a solid-state colorimage sensor of the type having color filters of a plurality ofdifferent colors formed above a plurality of photosensitive picturecells on a semiconductor substrate surface, comprises color filters offirst to third different colors including magenta, yellow and cyan;wherein color filters of said first color are used for color filterseach covering the entire area of a first type picture cell, and forcolor filters each covering a predetermined ratio of the entire area ofa second or third type picture cell; color filters of said second colorare used for color filters each covering the entire area of said secondtype picture cell, and for color filters each covering a predeterminedratio of the entire area of a fourth type picture cell; and colorfilters of said third color are used for color filters each covering theentire area of said third or fourth type picture cell.

The color filters covering predetermined ratios of the entire areas ofpicture cells are preferably formed collectively in a stripe shape.

The color filters covering predetermined ratios of the entire areas ofpicture cells may be formed as the upper layer on the lower color filterlayer covering the entire areas of picture cells.

According to another aspect of the present invention, a method ofmanufacturing a solid-state color image sensor of the type forming colorfilters of a plurality of different colors above a plurality ofphotosensitive picture cells disposed in a matrix configuration on asemiconductor substrate surface, comprises the following steps (a) to(e) which are carried out sequentially in an optional order and may ormay not include those steps carried out at the same time:

(a) forming a color filter of a first color at the position covering theentire area of a first type picture cell, said first color being one ofthe colors including magenta, yellow and cyan;

(b) forming a color filter of said first color at the position coveringa predetermined ratio of the entire area of a second or third typepicture cell;

(c) forming a color filter of a second color at the position coveringthe entire area of said second type picture cell, said second colorbeing another of the colors including magenta, yellow and cyan;

(d) forming a color filter of said second color at the position coveringa predetermined ratio of the entire area of a fourth type picture cell;and

(e) forming a color filter of a third color at the position covering theentire area of said third or fourth type picture cell, said third colorbeing the other of the colors including magenta, yellow and cyan.

According to the solid-state color image sensor of this invention, eachhalf area of the first to fourth type picture cell is covered with acolor filter of one of the colors including magenta, yellow and cyan,and the other half is covered with a color filter of another of thecolors including magenta, yellow and cyan. Therefore, it becomespossible to read image signals either at the field integration mode orat the frame integration mode, by properly selecting the positionalarrangement of the first to fourth type picture cells in the imagesensor. Further, since each picture cell is covered with two differentcolor filters, the vertical resolution of color signals can be improvedtwo times as good as that of an image sensor using one color filter perpicture cell. Furthermore, use of the complementary color filtersassures the sensitivity of the sensor without lowering it considerably,and use of cyan, yellow and magenta three colors retains a good colorreproductivity.

The following advantages can be obtained in manufacturing such asolid-state color image sensor: Since two different color filters areformed on a picture cell without integrally joining them asconventional, the manufacturing thereof is very easy. In addition, onesof the two different color filters for respective picture cells areformed collectively in a stripe shape above the picture cells to coverthe halves of the entire areas of picture cells. Therefore, even if theposition of the stripe color filter displaces up and down or right andleft to some degree, the stripe color filter can cover the halves of theentire areas of respective picture cells so long as the stripe colorfilter is positioned within the area of the picture cells, thusrealizing a stable spectrum characteristic.

Other objects and advantages of the invention will be apparent from thefollowing description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows the arrangement of color filters used in solid-state colorimage sensors heretofore proposed;

FIG. 2 is a partial plan view showing an embodiment of a solid-statecolor image sensor according to the present invention;

FIGS. 3 and 4 are cross sectional views taken along lines III--III andIV--IV of FIG. 2;

FIGS. 5A to 5C show spectrum characteristics of Mg, Cy and Ye colorfilters used in the present invention;

FIGS. 6A to 6C are schematic diagrams of the spectrum characteristicsshown in FIGS. 5A to 5C;

FIGS. 7A to 7D show output characteristics of picture cells respectivelyat areas (a) to (d) shown in FIG. 2;

FIGS. 8A to 8E are cross sectional views showing the processes of oneembodiment of the method of manufacturing the solid-state color imagesensor according to the present invention;

FIG. 9 is a partial plan view showing another embodiment of thesolid-state color image sensor according to the present invention;

FIG. 10 is a cross sectional view taken along line X--X of FIG. 9;

FIGS. 11A to 11E are cross sectional views showing the processes ofmanufacturing the solid-state color image sensor shown in FIG. 10; and

FIGS. 12A and 12B are partial plan views showing other embodiments ofthe solid-state color image sensor according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a partial plan view of an embodiment of a solid-state colorimage sensor according to the present invention, and FIGS. 3 and 4 arecross sectional views showing the internal construction of the imagesensor, respectively taken along lines III--III and IV--IV of FIG. 2.

The solid-state color image sensor is constructed as having colorfilters of a plurality of different colors formed on a solid-state imagesensor main body or semiconductor substrate with a plurality ofphotosensitive picture cells. Particularly, as shown in FIGS. 3 and 4,the semiconductor substrate 1 has photosensitive picture cells 2, 2, . .. such as photo diodes below the surface thereof. Each of thephotosensitive picture cells 2, 2, . . . is indicated by a broken-linerectangular in FIG. 2. Aluminum light-shielding films 3, 3, . . . areformed above the surface of the semiconductor substrate 1, the openingof the light shielding film 3 corresponding in position to thephotosensitive picture cell. Over the semiconductor substrate 1, atransparent layer 4 is formed within which Ye, Cy and Mg color filtersare sequentially formed, the colors being complementary colors of blue(B), red (R) and green (G). Particularly, as shown in FIGS. 2 and 4,rectangular Ye color filters 11 are formed at the 2nd and 4th columns atthe row (a) and at the 2nd and 4th columns at the row (d) to cover thewhole areas c and hence the entire areas of respective picture cells 2within the areas c. Ye color filters 12 in a stripe shape having a widthof a predetermined ratio, e.g. half, the picture cell width are formedat the rows (b) and (c) as shown in FIGS. 2 to 4, each Ye color filter12 traversing substantially at the center of each picture cell 2 andcovering a predetermined ratio, e.g. a half of the entire area of eachpicture cell within the areas b and d. As shown in FIGS. 2 and 4,rectangular Cy color filters 21 are formed at the 2nd and 4th columns atthe rows (b) and (c) to cover the whole areas d and hence the entireareas of respective picture cells 2 within the areas d. Cy color filters22 in a stripe shape having a width half the picture cell width areformed at the rows (a) and (d) as shown in FIGS. 2 to 4, each Cy colorfilter 22 traversing substantially at the center of each picture cell 2and covering a half of the entire area of each picture cell within theareas a and c. As shown in FIGS. 2 and 3, rectangular Mg color filters31 are formed at the 1st and 3rd columns to cover the whole areas a andb and hence the entire areas of respective picture cells within theareas a and b.

FIGS. 5A to 5C show the spectrum transmittance characteristics of Mg, Cyand Ye color filters of this invention, each of which shows an output ofeach picture cell 2 assuming that only one of Mg, Ye and Cy colorfilters covers the entire area of the picture cells shown in FIG. 2. Inother words, the Mg, Cy and Ye color filters are used which have beensubjected to the coloring to obtain the characteristics shown in FIGS.5A to 5C, respectively. The coloring density of Mg in particular has atransmittance of 40 to 60% at a wavelength of 550 nm.

FIGS. 6A to 6C are schematic diagrams showing the characteristics ofFIGS. 5A to 5C, respectively.

The transmittance characteristics at the areas a to d of the solid-statecolor image sensor with the color filters having the characteristics ofFIGS. 6A to 6C (5A to 5C) and constructed as shown in FIGS. 2 to 4 areshown in FIGS. 7A to 7D. Particularly, at the area a, a half of theentire area of the photosensitive picture cell 2 is covered with only Mgcolor filter 31 and the remaining half of the picture cell is coveredwith both Mg color filter 31 and Cy color filter 22. Therefore, thepicture cell 2 at the area a can be considered as being covered by acolor filter [Mg/2+(Mg+Cy)/2]. An output from the picture cell 2 at thearea a therefore becomes as shown in FIG. 7A which shows that the Rcomponent was cut by Cy as indicated by a broken line. Similarly,picture cells 2 at areas b to d are covered with color filters[Mg/2+(Mg+Ye)/2], [Ye/2+(Ye+Cy)/2]=[Ye/2+G/2)] and [Cy/2+(Ye+Cy)/2]=[Cy/2+G/2], respectively. The outputs from the picture cells2 at the areas b to d are shown in FIGS. 7B to 7D. An output shown inFIG. 7B indicates that the B component of Mg was eliminated by Ye, anoutput shown in FIG. 7C indicates that the R component of Ye waseliminated by Cy, and an output shown in FIG. 7D indicates that the Bcomponent of Cy was cut by Ye.

Since two different color filters are formed on each photosensitivepicture cell at each line of the solid-state color image sensor, itbecomes possible to read image signals not only in the field integrationmode but also in the frame integration mode. Moreover, each horizontalscan of picture cells can produce two different color difference signals[Mg/2+(Mg+Cy)/2]-[Ye/2+G/2] and [Mg/2+(Mg+Ye)/2]-[Cy/2+G/2], whereG=Ye+Cy, and also a constant value (Mg+Ye+Cy) can always be obtained asa luminance signal.

Thus, the vertical resolution of color signals can be obtained which istwo times as high as the conventional solid-state color image sensor.Such high resolution is particularly suitable for those solid-stateimage sensors of electronic still cameras which require a high verticalcolor signal resolution. Further, since complementary type color filtersare used, a high sensitivity can be maintained. Also, use of Cy, Ye andMg three colors enables a good color reproductivity in the linesequential color difference signal method.

The stripe filter with a half of the picture cell width can be formedwithin the area of the picture cell without failure so that a slightdisplacement of patterns hardly causes a change in ratio of areasoccupied by two different filters and hence a change in spectrumtransmittance, thus achieving a stable characteristic.

FIGS. 8A to 8E are cross sectional views each showing a differentprocess of an embodiment of a manufacturing method of the solid-statecolor image sensor. Each cross section showing the process correspondsto that taken along line VIII(E)-VIII(E) shown in FIG. 2. The embodimentof the method of manufacturing a solid-state color image sensor will bedescribed with reference to FIGS. 8A to 8E.

Referring to FIG. 8A, reference numerals 1 to 3 denote the same elementsdescribed previously. Namely, reference numeral 1 denotes asemiconductor substrate, 2 a photosensitive picture cell, and 3 analuminum light-shielding film. A transparent layer (base layer) 4a ofacrylic resin type is formed on the solid-state image sensor constructedof the elements 1 to 3. The transparent layer 4a makes flat the unevensurface of the semiconductor substrate 1 caused during the waferprocess, and serves to tightly contact thereon a coloring resist forcoloring it into Ye at the succeeding process.

Next, as shown in FIG. 8B, a coloring resist layer 10 such as caseinhaving a coloring function is formed on the transparent layer 4a. Thecoloring resist layer 10 is used for forming the Ye color filters 11 and12 by patterning it by means of the photo engraving process (PEP) andleaving only the necessary portions. The left coloring resist layer issubjected to coloring by using an Ye coloring liquid to thereby form theYe color filters 11 and 12.

Next, as shown in FIG. 8C, formed on the Ye color filters 11 and 12 andthe transparent layer 4a is a transparent resist layer 4b of acrylicresin type similar to the transparent layer 4a. On the transparent layer4b, a coloring resist layer 20 like the coloring resist layer 10 isformed. The coloring resist layer 20 is used to form the Cy colorfilters 21 and 22 by patterning it by the PEP similar to the case of thecoloring resist layer 10 and leaving only the necessary portions. Theleft coloring resist layer is subjected to coloring by using a Cycoloring liquid to thereby form the Cy color filters 21 and 22.

Thereafter, as shown in FIG. 8D, formed on the Cy color filters 21 and22 and the transparent layer 4b is a transparent resist layer 4c ofacrylic resin type similar to the transparent layers 4a and 4b. On thetransparent layer 4c, a coloring resist layer 30 like the coloringresist layers 10 and 20 is formed. The coloring resist layer 30 is usedto form the Mg color filter 31 by patterning it by the PEP similar tothe case of the coloring resist layers 10 and 20 and leaving only thenecessary portions. The left coloring resist layer is subjected tocoloring by using an Mg coloring liquid to thereby form the Mg colorfilter 31. Thereafter, formed on the Mg color filter 31 and thetransparent layer 4c is a transparent layer 4d like the transparentlayers 4a to 4c. The transparent layer 4d serves as an over-coat(passivation) layer.

In the method of manufacturing the solid-state color image sensoraccording to the present invention, two different color filters perpicture cell are independently formed without adopting the method ofintegrally joining two different color filters on a picture cell asconventional. Therefore, each color filter can be formed easily.Specifically in forming a color filter covering a half of the entirearea of each picture cell, a stripe shape color filter is used so thateven the position of the color filter displaces up and down or right andleft, a half of the entire area of the picture cell is always coveredwith the stripe color filter so long as it is positioned within theentire area of the picture cell. As a result, a solid-state color imagesensor having a stable spectrum characteristic can be formed with ease.

FIG. 9 shows another embodiment of the solid-state color image sensoraccording to the present invention. The embodiment shown in FIG. 9 hasthe same construction except that the positional order of areas a to dis different from the embodiment shown in FIG. 1. As the manufacturingmethod for this embodiment, the method as described with FIG. 8 may beused.

In the above manufacturing method, the Ye color filters 11 and 12 areformed at the same time, and the Cy color filters 21 and 22 are alsoformed at the same time. However, in case where a sufficient resolutionof the coloring resist layers 10 and 20 for forming the Ye and Cy colorfilters cannot be obtained, the Ye filters 11 and 12 may be formedindependently, and the Cy color filters 21 and 22 may also be formedindependently.

FIG. 10 is a cross sectional view of the solid-state color image sensorformed in accordance with the above-described, the latter manufacturingmethod, the sectional view being taken along line X--X of FIG. 9.

In the solid-state color image sensor shown in FIG. 10, the Cy colorfilter 21 covering the entire area of a picture cell is formedindependently from the other Cy color filter 22 covering a half of theentire area of a picture cell, as is different from the case shown inFIG. 4. This arrangement is suitable for obtaining a fine pattern of avery high density solid-state image sensor.

In the embodiment shown in FIG. 9, the underlying Mg, Cy and Ye colorfilters are formed in units of two vertically consecutive picture cellsfrom the standpoint of manufacturing simplicity. However, all adjacentcolor filters may use a different color on condition that the Mg and Cycolor filters and the Mg and Ye color filters are respectively disposedin the direction along each line.

FIGS. 11A to 11E are cross sectional views each showing a differentprocess of the manufacturing method of this invention by which the imagesensor having the structure just mentioned above can be realized. First,a transparent layer 4 called a base layer is formed over the surface ofa substrate 1 whose photoelectric conversion areas, light-shieldingareas (both not shown) and polysilicon wire layers 5 and 6 have beenformed already (FIG. 11A). The base layer 4 eliminates the surfaceunevenness caused during the wafer process, and also improves the tightcontact with a coloring resist at the next process.

Next, a coloring resist whose main components are casein or the like iscoated over the whole surface, which resist is patterned to leave onlythe necessary portions. The left portions are subjected to coloring toyellow to thus obtain an yellow layer 11 (FIG. 11B).

Succeedingly, an intermediate transparent layer 7 is formed on the wholesurface to then coat a second coloring resist which is patterned toleave only the necessary portions. The left portions are subjected tocoloring to cyan to obtain a cyan layer 21 (FIG. 11C).

Next, a similar, intermediate transparent layer 8 is formed on the wholesurface. A third coloring resist coated upon the transparent layer 8 ispatterned to leave the necessary portions. The left portions are subjectto coloring to magenta to obtain a magenta layer 9 (FIG. 11D). Thedensity of coloring to magenta is half the density required for a singlemagenta layer. In order to obtain the density as small as a half, thedipping time into the coloring liquid may be made half or the density ofthe coloring liquid may be made half.

In the similar manner as above, an intermediate layer 9, a second yellowlayer 12, an intermediate layer 10, and a second cyan layer 22 aresequentially formed and lastly, an over-coat layer 14 serving as apassivation layer is formed to complete the color filter manufacturingprocess.

The order of forming color filter layers is not limited to the aboveembodiment only. Patterning the color filter may be performed after orbefore the coloring.

FIGS. 12A and 12B are partial plan views showing other embodiments ofthe solid-state color image sensor according to the present invention,wherein the left side upper corners of FIG. 2 are partially shown.Instead of the stripe-shaped color filters 22 and 12 shown in FIG. 2,circular color filters 22A and 12A as shown in FIG. 12A or rectangularcolor filters 22B and 12B as shown in FIG. 12B may be used. Obviously,the area of each color filter 22A, 22B, 12A or 12B is a half of theentire area of each picture cell.

As described above, the ratio of areas occupied by two color filters ina picture cell is generally half. However, a ratio other than half maybe also used according to variations in filter material, thickness,color density, etc.

What is claimed is:
 1. A solid-state color image sensor having aplurality of photosensitive picture cells disposed in a matrixconfiguration on a semiconductor substrate surface, and pairs of twodifferent color filters per each picture cell, the area of each colorfilter being a predetermined ratio of area of each picture cell, thecolor filters having first to third colors each representative ofmagenta, yellow or cyan, and producing pairs including a pair of magentaand cyan, a pair of cyan and green, a pair of green and yellow, and apair of yellow and magenta, wherein:color filters of said first coloreach covering the entire area of a first type picture cell, and coveringa predetermined ratio of the entire area of a second or third typepicture cell; color filters of said second color each covering theentire area of said second type picture cell, and covering apredetermined ratio of the entire area of a fourth type picture cell;color filters of said third color each covering the entire area of saidthird or fourth type picture cell; and the color filters covering thepredetermined ratios of the entire areas of respective picture cells areformed collectively in a stripe shape traversing substantially at thecenter of each picture cell on the same line.
 2. A solid-state colorimage sensor according to claim 1, wherein said predetermined ratio is ahalf.
 3. A solid-state color image sensor of the type adopting a linesequential color difference signal method and having a plurality ofphotosensitive picture cells disposed in a matrix configuration on asemiconductor substrate surface, and pairs of two different colorfilters per each picture cell, the area of each color filter being apredetermined ratio of the area of each picture cell, the color filtersproducing pairs including a pair of magenta and cyan, a pair of cyan andgreen, a pair of green and yellow, and a pair of yellow and magenta,wherein said color filters include a stripe-shaped second cyan colorfilter formed on the upper layer of a layer where yellow color filtersand magenta color filters with a predetermined ratio of density arealternately disposed in alignment with a line, and a stripe-shapedsecond yellow color filter formed on the upper layer of a layer wherecyan color filters and magenta color filters with twice thetransmittance are alternately disposed in alignment with a line, saidstripe-shaped filter formed on the upper layer having a width of apredetermined ratio that of an opening formed in said layer withalternative color filter arrangement, and wherein the color filters areformed collectively in a stripe shape traversing substantially at thecenter of each picture cell on the same line.
 4. A solid state colorimage sensor according to claim 3, wherein said predetermined ratio is ahalf.